The embodiments described herein relate generally to industrial emissions control systems and, more particularly, to an arrangement for a catalyst in an industrial emissions control system.
At least some know industrial systems that combust hydrocarbon fuels, such as gas turbines, industrial boilers and furnaces, and reciprocating engines, generate pollutants such as, but not limited to, carbon monoxide (CO), unburned hydrocarbons (UHC), and oxides of nitrogen (NOx). Emissions of such pollutants into an ambient atmosphere must be limited for safe operation.
One known technology for use in controlling stack emissions is Selective Catalytic Reduction. Selective Catalytic Reduction (SCR) is a method of reducing an amount of NOx and CO in the exhaust gas of fossil fuel-fired industrial and electric utility equipment. In at least some known SCR systems, anhydrous ammonia is mixed with the exhaust gas, and the mixture is channeled over a suitable reduction catalyst at a suitable temperature prior to being released into the atmosphere. For example, the catalyst is an active phase of vanadium pentoxide on a carrier of titanium dioxide. The catalyst is typically provided as a plurality of catalyst elements, such as honeycomb shaped substrates, arranged in a vertically and transversely extending wall perpendicular to the flow of oncoming exhaust gas.
In at least some cases, a total surface area of the catalyst required to reduce pollutant concentration necessitates that a height and width of the wall be quite large, relative to a duct that supplies the exhaust gas to be treated. A depth of the catalyst elements may be limited due to a pressure drop caused by gas travel through the catalyst elements, eliminating increased wall depth as an option to increase catalyst surface area. Moreover, space in industrial systems is typically limited and/or expensive, necessitating as small of a footprint as possible for the SCR system. As a result, an inlet duct of at least some known SCR systems inclines steeply in height as it approaches the wall of catalyst elements. However, the rapid change in cross-sectional area of the inlet duct may result in flow separation and/or recirculation zones, which in turn increases pressure drop and/or non-uniformity of gas flow temperature and velocity over the catalyst. As a result, performance of the catalyst may vary across the wall, and a useful lifetime of some catalyst elements may be reduced. Moreover, in at least some cases, a height of an upstream ammonia injection grid and/or a height of a downstream exhaust stack must be designed to accommodate the height of the wall.